The present disclosure identifies particular references by numerical designation. The references are specifically identified herein following the detailed description of exemplary embodiments. It has been known to measure voltages using optical means.
Some known optical voltage measurement techniques, such as those described in Refs. 1-3 identified below, rely on the piezoelectric effect. In these devices, a field-induced mechanical change in a piezoelectric material leads to stress in an optical sensing element (such as a fiber) that is mechanically coupled to the piezoelectric material. The stress, in turn, leads to a voltage-induced change of birefringence in the sensing element, which can be detected optically.
Other known optical voltage measurement techniques, such as that described in Ref. 10 identified below, rely on the electro-optic effect, in which an electric field changes the refractive index or birefringence of a material directly, e.g., through the linear Pockels effect.
In both techniques, a measurement of the phase delay (or a change thereof) between two orthogonally polarized light waves allows measurement of the electric field strength, or, more accurately, the integral of the same along the path of the light.
It has also been known to measure current by means of similar techniques, see, e.g., Refs. 5-7 identified below, in which a magnetic-field induced phase shift between left and right circularly polarized light waves in a fiber is measured by means of a suitable control unit.